I. Field of the Invention
This invention relates to lighting or indicator devices intended for motor vehicles in particular. Lighting devices mainly comprise the lamps for dipped, main, fog or running lamps, and the indicator lamps mainly comprise position lamps, direction change indicator lamps, braking indicator lamps, reversing lamps, and rear fog lamps.
In order to simplify location of these various devices on a vehicle it is normal practice to group several together in a single housing, which in particular makes it easier to install them on the vehicle, and to connect them to the vehicle's electrical loom using a single connector provided with an appropriate number of terminals.
Each function generally incorporates a light source, a reflector reflecting the light rays emitted by the source in a general direction of emission, and possibly an enclosing glass, also called an indicator, which may or may not contribute to formation of the light beam, these various components being designed to provide a lighting or indicator beam whose geometrical and photometric characteristics must comply with various regulations. The glass enclosing the housing or indicator is generally common to all the devices present in the same housing.
Each function thus requires a minimum space for location within the individual lighting or indicator device. However the volume available for locating lighting or indicator devices both at the front and rear of a modern motor vehicle is increasingly smaller. In fact the constraints of aerodynamics and stylistic design lead to shapes which are often very different from those which would result from technical considerations alone.
It follows that in many cases three constraints apply simultaneously to the designers of lighting or indicator devices:
i) the light beams must be emitted parallel to the longitudinal axis of the vehicle,
ii) the glass enclosing the housing must have a shape which may at the same time be highly curved and highly inclined in relation to the vertical, and
iii) the volume available within the housing for locating the various optical systems is relatively small.
It is possible to provide lighting or indicator devices in which the light sources, such as electroluminescent diodes, are positioned on a flat surface, with or without a reflector, and with or without diffusing screens, regardless of the external shape of the lighting or indicator device or its enclosing glass. Although such a design is of low cost, it is unable to provide lighting or indicator devices whose styling is suitable for modern vehicles.
Furthermore, if it is desired for example to provide an indicator lamp which is curved in at least one direction, it is generally provided that the light sources are arranged in such a way that the electroluminescent diodes are located in a regular arrangement, i.e. in a matrix of lines and columns when seen from the front. Such design is relatively constricting. Furthermore, if the lighting or indicator device has a curvature in two directions it is in most cases necessary to bend the surface supporting the light sources in two directions, which is relatively complicated.
II. Description of the Related Art
Various solutions have already been suggested in order to overcome these problems. For example a collimating optical component for an indicator lamp which is designed to be associated with a supporting member having electroluminescent diodes incorporating a dorsal surface which acts together with these electroluminescent diodes, the dorsal surface being shaped in steps onto which transverse openings associated with the electroluminescent diodes open, is known from document FR-A-2 680 859.
Such design makes it possible to design a robust optical element, the diodes being located in the appropriate places. They are supported on strips belonging to the supporting member which usually comprises such an indicator lamp. The diodes may also be located as a sandwich between the strips and the steps so that the diodes can be located in the appropriate position, in particular at the focus or optical centre of the openings in the collimating element, despite the awkward shape of the indicator lamp.
It has already been suggested in document EP-A-1 110 817 that an electroluminescent diode power circuit which may have a curved shape, possibly in two different planes, might be constructed instead of a matrix arrangement based on a flat plane. Such a process for the manufacture of an electroluminescent diode power circuit located on planar supports which are parallel to each other comprises the stages of:                determining the relative positions of the supports,        determining whether there is a set of planes perpendicular to the supports, which are parallel to each other, each of which passes through at least one support and such that in each plane the supports have corresponding coordinates relating to a first axis perpendicular to the support which vary uniformly with their abscissas along a second axis parallel to the supports and the planes,        determining a reference plane parallel to the supports,        determining the image of each support by a projection following the same projection axis on the reference plane followed by translation in relation to the second axis by a length equal to the distance of the support along the projection axis, and        linking the images by connecting branches located within the reference plane.        
This document also discloses a base for a power circuit for electronic components such that electroluminescent diodes, which are for example constructed using the process which has just been mentioned, and comprising supports for components, the base being of flat shape, the supports being located in such a way that it is possible to make cut-outs in the base so that by forming folds which are parallel to each other the base can be given a shape such that the supports are planar and parallel with each other, and at least some supports are intercepted by a single plane parallel to the folds and perpendicular to the supports, are not coplanar.
Such a process is relatively complex to implement, and requires thorough investigation of the location of the lamp to determine the lines for folding the base for its electrical power circuit. It follows that the lighting or indicator devices so obtained offer greater development possibilities for the stylists, but have relatively high costs which restrict their use to top-of-the-range vehicles.